For many builders, the reluctance to install hardwood floors over radiant heat stemmed from problems associated with the original technology introduced more than forty years ago. Then, floors were heated excessively to compensate for poor building insulation. Those high temperatures exaggerated expansion and contraction in hardwood flooring, causing irreparable damage to both the floors and builders' reputations.
MOISTURE CONTENT   Once the sub floor, tubing and thermostats have been installed, the heating system should be run for at least 72 hours to balance the house's moisture content. Now follow the customary procedures for installing any hardwood floor. Be sure to monitor the moisture content of both the sub floor and the flooring, because this can have a profound effect on the end result of your installation.     
SLABS
   The slab should be dried with heat before installing a hardwood floor. Never install wood flooring over a concrete floor until you have turned on the floor heating system to remove any residual moisture from the slab.           The easiest method to test a slab for moisture is to tape a 4 ft. x 4 ft. section of polyethylene plastic sheeting to the slab and turn on the heat overnight.  If moisture appears under the plastic, heat the slab another day and test again. Repeat this test until no moisture appears.
PLYWOOD SUB FLOORS   Do not deliver the flooring until, you have turned on the heating system, the plywood is dry and the room has reached the proper relative humidity.

IN DRY CLIMATES THE RELATIVE HUMIDITY MUST BE MAINTAINED AT 45% TO PROTECT HARD WOOD FLOORS FROM GETTING TOO DRY.

  Wood naturally expands and contracts to reach balance with the relative humidity of its surroundings. That's why it's important to avoid installing wood flooring when moisture levels typically rise sharply, especially during painting or the installation of sheet rock. When radiant heat is installed in concrete, mortar beds or gypsum cement, operate the heating system until these are completely dry before topping with wood floors. This can take several weeks.
Before hardwood floor installation, operate the heating system until the relative humidity in the space stabilizes to the average level expected for seasonal conditions in the area in which the wood floor will be installed. For example, if the space is expected to average 30 percent relative humidity in the winter and 50 percent in the summer, the average would be 40 percent. In especially dry regions like the American Southwest, a humidifier may be recommended, Likewise, a dehumidifier may be needed in especially humid climates.
   Experienced flooring installers will ensure that the wood floor's moisture content is appropriate for your area. The surface of the wood floor should not exceed 85 degrees Fahrenheit at the time of installation. Turning the system on at least five to six days in advance also ensures that there are no leaks, it works properly, and the house's moisture content is balanced. Moisture testing, not a timeline, is the best indicator of a job's readiness to receive the hardwood flooring.
  Care and maintenance  Caring for a hardwood floor with radiant heat is no different than caring for any other hardwood floor. Radiant heat systems also typically have no effect on refinishing guidelines. (It is, however, always best to check with the finish manufacturer.) When coating or finishing the hardwood floor, the radiant heat system should be turned off about six hours in advance so that the floor is at a normal temperature to avoid applicator marks or bubbles. When the coating is completely dry, it is safe to turn the system back on.

PLY WOOD AND STRAND BOARD ARE NOT AFFECTED BY RADIANT FLOORS
NEVER USE UN-VENTED GAS OR OIL SPACE HEATERS TO DRY THE ROOMS !

REMEMBER SLABS MUST HAVE A MOISTURE BARRIER UNDER THEM